Interleaved electrodes for touch sensing

ABSTRACT

A capacitive touch sensing system includes a touch surface and sets of substantially parallel electrodes arranged in relation to the touch surface. Each electrode set includes a primary electrode electrically connected to at least two sub-electrodes. The primary electrode is capable of producing greater capacitive coupling to a touch in proximity with the touch surface in relation to capacitive coupling of the at least two sub-electrodes. The sub-electrodes of the electrode sets are arranged in an interleaved pattern configured to increase an effective area of capacitive coupling associated with each electrode set.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. Ser. No. 11/243,534, filed Oct.5, 2005, now U.S. Pat. No. 7,864,160 now allowed, the disclosure ofwhich is incorporated by reference in its entirety herein.

FIELD OF THE INVENTION

The present invention relates to methods and systems for sensing a touchin proximity with a touch surface.

BACKGROUND

Electronic displays are widely used. Although in the past the use ofelectronic displays has been primarily limited to computing applicationssuch as desktop computers and notebook computers, as processing powerhas become more readily available, such capability has been integratedinto a wide variety of applications. For example, it is now common tosee electronic displays in applications such as teller machines, gamingmachines, automotive navigation systems, restaurant management systems,grocery store checkout lines, gas pumps, information kiosks, andhand-held data organizers to name a few.

Interactive visual displays often include some form of touch sensitivescreen. Integrating touch sensitive panels with visual displays isbecoming more common with the emergence of portable multimedia devices.Capacitive touch sensing techniques for touch sensitive panels involvesensing a change in a signal due to capacitive coupling created by atouch on the touch panel. An electric field is applied to electrodes onthe touch panel. A touch on the touch panel couples in a capacitancethat alters the electric field in the vicinity of the touch. The changein the field is detected and used to determine the touch location.

Increasing the accuracy and/or decreasing the processing time of touchlocation determination is desirable. The present invention fulfils theseand other needs, and offers other advantages over the prior art.

SUMMARY OF THE INVENTION

The present invention is directed to touch sensing systems and methods.In accordance with one embodiment, a capacitive touch sensing systemincludes a touch surface and sets of substantially parallel electrodesarranged in relation to the touch surface. Each electrode set includes aprimary electrode electrically connected to at least two sub-electrodes.The primary electrode is capable of producing greater capacitivecoupling to a touch in proximity with the touch surface in relation tocapacitive coupling of the at least two sub-electrodes. Thesub-electrodes of the electrode sets are arranged in an interleavedpattern configured to increase an effective area of capacitive couplingassociated with each electrode set.

According to one aspect of the embodiment, the interleaved pattern isconfigured to shape touch response profiles respectively associated withthe electrode sets. Each touch response profile is representative of arelationship between touch signal amplitude and touch position relativeto a particular electrode set. According to another aspect, theinterleaved pattern is configured to modify a slope of each touchresponse profile. In one implementation, a width of the primaryelectrode or a width of the sub-electrodes of an electrode set may beconfigured to shape the touch response profiles of each electrode set.In another implementation, a spacing between the primary electrode andat least two sub-electrodes of each electrode set is configured to shapethe touch response profiles of the electrode sets.

According to yet another aspect of the embodiment, the interleavedpattern is configured to increase a region of linearity of the touchresponse profiles respectively associated with the electrode sets, eachtouch response profile representing a relationship between touch signalamplitude and touch position relative to a particular electrode set. Inone example, the interleaved pattern may be configured to facilitateinterpolation among touch signals sensed using the adjacent electrodesets to facilitate touch location determination. In another example, theinterleaved pattern is configured to smooth a touch signal transition asthe touch is moved from one electrode set to another electrode set. Theinterleaved pattern enables interpolation at the edges of the touchsurface by electrically connecting a sub-electrode near one edge of thetouch surface with a corresponding primary electrode near an oppositeedge of the touch surface. This can improve the accuracy of thecoordinate determination at the edges of the sensor.

The primary electrode may be electrically connected to the correspondingsub-electrodes of the electrode set at one or both ends of the primaryelectrode. The electrode sets may be further electrically connected in acoding scheme to facilitate touch location determination.

In one configuration, the electrode sets are arranged on a single layer.In another configuration, the electrode sets are arranged on first andsecond layers, a longitudinal axis of the electrode sets of the firstlayer arranged at an angle with respect to a longitudinal axis of theelectrode sets of the second layer. For example, the longitudinal axisof the electrode sets of the first layer may be substantially orthogonalto the longitudinal axis of the electrode sets of the second layer.

The interleaved pattern may comprise a repetitive pattern and/or mayinvolve single or multiple levels of interleaving. A single level ofinterleaving may involve one sub-electrode of each electrode setinterleaved with one sub-electrode of a neighboring electrode set.Multiple levels of interleaving may involve two or more sub-electrodesof each electrode set interleaved with two or more sub-electrodes of anadjacent electrode set.

The touch sensing system may further comprise circuitry configured tomeasure signals sensed using the electrode sets and a touch processorcoupled to the sensor circuitry and configured to determine a locationof the touch in proximity with the touch surface based on the measuredsignals. In some implementations, at least a portion of the sensorcircuitry can be disposed within a touch implement, for example providedin the form of a stylus. The touch surface and the sets of electrodesmay form a transparent touch screen. The touch sensing system mayfurther comprise a display viewable through the transparent touchscreen.

Another embodiment of the invention is directed to a capacitive touchsensing system including a touch surface and sets of electricallyconnected and substantially parallel electrodes arranged in relation tothe touch surface. Each set of electrodes includes a primary electrodeand at least two sub-electrodes disposed on either side of the primaryelectrode and having a smaller surface area than the primary electrode.The sub-electrodes of the electrode sets are interleaved.

In one implementation, the width of each primary electrode and/or thewidth of each sub-electrode varies along a longitudinal axis of theprimary electrode or sub-electrode. The electrode sets may be disposedon two layers, wherein electrodes on a first layer include geometricelements, and electrodes on a second layer include geometric elementscomplementary with the geometric elements of the first layer electrodes.The complementary geometric elements of the first and second layerelectrodes are configured to enhance capacitive coupling of the secondlayer electrodes.

In one implementation, the primary electrode of each electrode set maycomprise a first number of adjacent electrode elements havingsubstantially equal width and the sub-electrodes of each electrode setmay comprise a second number of adjacent electrode elements havingsubstantially equal width.

Another embodiment of the invention is directed to a touch sensingmethod. A touch in proximity with a touch surface is capacitively sensedusing a first set of electrodes. The first set of electrodes includeselectrically connected and substantially parallel first primaryelectrode and first sub-electrodes disposed on either side of the firstprimary electrode. A first touch signal is generated based on the touchsensed using the first electrode set. The touch is capacitively sensedusing one or more sets of electrodes adjacent to the first electrodeset. Each adjacent set of electrodes includes electrically connected andsubstantially parallel adjacent primary electrode and adjacentsub-electrodes disposed on either side of the adjacent primaryelectrode. The adjacent sub-electrodes are interleaved with the firstsub-electrodes to increase an area of capacitive coupling of the firstand adjacent electrode sets. One or more additional touch signals aregenerated based on the touch sensed using the one or more adjacent setsof electrodes. A location of the touch is determined based on at leastone of the first and the one or more additional touch signals.

According to one implementation, determining the location of the touchmay involve interpolating among the first and the one or more additionaltouch signals. In various configurations, the touch may be a fingertouch, may be produced by an electrically passive touch implement, ormay be produced by an electrically active touch implement.

Yet another embodiment of the invention is directed to a method formaking a touch sensor. The method includes disposing sets of electrodeson a substrate in accordance with an interleaved pattern configured toincrease an effective area of capacitive coupling associated with eachset of electrodes. Each set of electrodes includes a primary electrodedisposed between at least two sub-electrodes electrically connected andsubstantially parallel to the primary electrode. The primary electrodeis capable of producing greater capacitive coupling to a touch inrelation to capacitive coupling of the at least two sub-electrodes.

The above summary of the present invention is not intended to describeeach embodiment or every implementation of the present invention.Advantages and attainments, together with a more complete understandingof the invention, will become apparent and appreciated by referring tothe following detailed description and claims taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a plan view of a matrix touch screen;

FIG. 2A illustrates touch response profiles produced by a regularpattern of electrodes;

FIG. 2B illustrates a cross section view of the matrix touch screen ofFIG. 1;

FIGS. 3A and 3B illustrate a plan view and a cross sectional view of atouch screen having electrodes arranged in an interleaved pattern inaccordance with embodiments of the invention;

FIG. 4 illustrates touch response profiles of the five primaryelectrodes of the touch screen of FIGS. 3A and 3B;

FIG. 5 illustrates touch response profiles of the primary electrodes andsub-electrodes of the touch screen of FIGS. 3A and 3B, withinterconnections 71-75 and 91-95 removed;

FIG. 6 illustrates touch response profiles of the primary electrodes andsub-electrodes of the touch screen of FIGS. 3A and 3B, interconnected asshown in FIG. 3A, with a thick overlay;

FIG. 7 is a plan view of a touch sensor having two levels of interleavedsub-electrodes in accordance with embodiments of the invention;

FIG. 8 illustrates touch response profiles of the primary electrodes andsub-electrodes of the touch screen of FIGS. 3A and 3B, interconnected asshown in FIG. 3A, with a thin overlay;

FIG. 9 illustrates touch response profiles of electrodes of variouswidths, with a thick overlay;

FIG. 10 illustrates touch response profiles of electrodes of variouswidths, with a thin overlay;

FIG. 11 illustrates a touch sensor having interleaved electrodesproviding a transition from the one edge of the touch sensor to anotheredge in accordance with embodiments of the invention;

FIGS. 12A, 12B, and 13A-13E illustrate configurations for interleavedelectrodes in accordance with embodiments of the invention;

FIG. 14 illustrates primary electrodes and sub-electrodes comprisingmultiple parallel elements in accordance with embodiments of theinvention;

FIG. 15 illustrates electrode sets that are connected in accordance witha coding scheme in accordance with embodiments of the invention; and

FIG. 16 illustrates a touch sensing system that may incorporate a touchscreen having interleaved electrodes in accordance with embodiments ofthe invention.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It is to be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

In the following description of the illustrated embodiments, referenceis made to the accompanying drawings that form a part hereof, and inwhich is shown by way of illustration, various embodiments in which theinvention may be practiced. It is to be understood that the embodimentsmay be utilized and structural changes may be made without departingfrom the scope of the present invention.

In various implementations, capacitive touch sensors may include a layerof substantially parallel electrodes, or may include first and secondlayers of substantially parallel electrodes, or may include a firstlayer of electrodes with a planar electrode disposed on a second layer,or may include other electrode configurations. Touch sensing involvesdetecting changes in electrical signals present at the electrodes in thevicinity of a touch. In some implementations, the touch sensor may use afirst layer of parallel electrodes to sense the touch location in theY-direction and a second layer of parallel electrodes, arrangedsubstantially orthogonally to the first layer electrodes, to detect thetouch location in the X-direction. The X and Y electrodes may be drivenwith applied electrical signals, or an active stylus may couple signalsonto electrodes. A touch to or near the touch surface may capacitivelycouple X and Y electrodes in the vicinity of the touch to ground, or atouch may capacitively couple signal from one electrode to an adjacentelectrode. A touch to or near the touch surface may capacitively couplea transmitter stylus signal to X and Y electrodes in the vicinity of thetouch. The capacitive coupling causes a change in the electrical signalon the electrodes near the touch location. The amount of capacitivecoupling to each electrode, and thus the change in the signal on theelectrode or in a receiver stylus, varies with the distance between theelectrode and the touch. The X and Y touch location may be determined byexamining the changes in the electrical signals detectable on the X andY electrodes or in a receiver stylus.

Accurate determination of the touch location involves processing signalssensed on multiple electrodes in the vicinity of the touch. For example,touch signal processing may include interpolation among signal valuessensed on two or more electrodes in the vicinity of the touch. Thus,information acquired from the most altered signal sensed on theelectrode nearest to the touch may be combined with additionalinformation acquired from signals sensed on electrodes farther away fromthe touch location.

The present invention is directed to the use of interleaved andinterconnected electrodes to shape a touch signal profile to enhancetouch signal processing for touch location determination. A touch signalprofile defines a relationship between touch signal amplitude anddistance from the touch position to the electrode used to sense thetouch signal. In accordance with various embodiments of the invention,the interleaved pattern of electrodes is arranged to modify a slopeand/or to increase a region of linearity of the touch response profile.The modification of the touch response profile produced by theinterleaved electrodes enhances interpolation of touch signals toprovide simpler and more accurate touch location determination.

The embodiments described below are based on matrix capacitive touchtechnology, although the concepts are equally applicable to other typesof capacitive touch sensors that employ one or more layers ofsubstantially parallel electrodes, including for example thesingle-layer sensors described in commonly owned U.S. Pat. No. 6,825,833which is incorporated herein by reference. Matrix capacitive touchsensors known in the art typically use two layers of electrodes, a toplayer of electrodes 11-20 arranged orthogonally to a bottom layer ofelectrodes 22-27 as illustrated in plan view in FIG. 1 and in crosssection in FIG. 2B. As shown in FIG. 2B, the top layer electrodes 11-20have width W_(B) and spacing P_(B). The electrodes 11-20 and 22-27 maybe connected to controller electronics (not shown) through bus lines(not shown) and touch measurement ports (TMPs) (also not shown). Thecontroller may provide drive/sense circuitry for measuring the signalchanges on the electrodes or in a stylus, in response to a touch on thetouch sensor. The controller may also include a touch processor capableof determining the touch location based on the measured signal changes.

FIG. 2B depicts cross section AA of sensor 10, including a first layerof electrodes 12-15. Electrode 27 represents one of the lower electrodesof the matrix, which are substantially orthogonal to electrodes in sets12-15. A touch by a touch implement, such as a finger or stylus,provides capacitive contact between one or more of electrodes 12-15 andelectrical ground, not shown. FIG. 2A shows touch response profilecurves 62-65 representing magnitudes of signal coupling from a touch toelectrodes 12-15 with respect to the touch position. As the touch moveson or near surface 33 across each electrode, signal coupling increasesto a maximum when the touch is directly over an electrode; then themagnitude decreases as the distance between the electrode and the touchincreases. The shape of each touch response profile 62-65 depends on thewidth of the electrode, the width and shape of the touch implement, andthe minimum distance 34 between the touch implement and an electrode,which is typically the thickness of overlay 51.

Touch response profiles 62-65 of FIG. 2A are associated with the amountof capacitive coupling vs. distance between the touch and the electrode.Slopes of profiles 62-65 indicate a rate of change of touch signalmagnitude (i.e. the amount of coupling) vs. touch implement position inthe plane of surface 33. A touch at point 75 couples most strongly toelectrodes 12 and 13. Movement of the touch in the positive X directionresults in an increase of signal 63 and decrease of signal 62. Curvefitting or interpolation of signals 62 and 63 may be used to calculatethe position of the touch between electrodes 12 and 13. Sensitivity(accuracy and resolution) of the curve fit or interpolation will be afunction of the slopes and relative positions (e.g., degree of overlap)of curves 62 and 63.

For example, the slope of curve 62 for a touch at point 75 is −18°, andthe slope of curve 63 is +18°. For purposes of illustration, equalgraphical units are assigned to the horizontal and vertical axes of FIG.2A, so an 18° slope yields 0.32 units of change in amplitude in curve 62for each unit of horizontal movement of a touch. Curve 63 has anapproximately equal and opposite amplitude change so positionsensitivity is 0.64 as calculated by Equation 1, where Equation 1 is asimplified approximation of sensitivity that may be achieved by atypical interpolation algorithm, to wit:Position sensitivity (PS)≅(|Δ signal 1|+|Δ signal 2|)/|Δ touchposition|  (1)where “Δ signal 1” represents the change in the touch signal amplitudemeasured using a first electrode, “Δ signal 2” represents the change inthe touch signal amplitude measured using a second electrode, and “Δtouch position” represents the change in the touch position. At point76, curve 63 has a slope of zero, so curve 63 magnitude is insensitiveto touch movement, and an incremental change in the position of thetouch will not change the signal magnitude significantly. Curves 62 and64 may be used to increase the sensitivity of a touch positioncalculation. The slopes of curves 62 and 64 are +11° and −11°respectively for point 76, yielding a combined sensitivity of 0.38according to Equation 1. This is the lowest positional sensitivity pointon the touch surface, so the resolution of position calculations will belowest for point 76 even though the presence of a touch is sensed verystrongly, as indicated by the large magnitude of curve 63 correspondingto point 76.

A touch at point 77 yields relatively high sensitivity due to thesteep)(−84° slope of curve 62 at that point. While interpolation betweencurve 62 and curve 63 is quite sensitive to touch implement horizontalposition at point 77, the differences in slope between curve 62 and 63makes X position calculation by linear interpolation inaccurate. Anon-linear interpolation is preferred, to account for the differences inslopes of curves such as 62 and 63.

Sensitivity could be improved by moving electrodes 12-15 closertogether, resulting in increased overlap of curves 62-65 and increasedslopes of curves in the areas where interpolation is required. But,additional electrodes would be required to cover a given area. Thisrequires additional processing circuitry for the additional electrodes.Connecting each of the electrodes 11-20 and 22-27 to the controllerthrough a separate signal lines and TMP allows for individual sensing ofeach electrode. However, in larger touch screens, the number ofelectrodes prohibits individual sensing.

A touch sensing system having sets of electrodes arranged in aninterleaved pattern in accordance with embodiments of the invention isillustrated in FIGS. 3A and 3B. FIG. 3A shows one layer of a matrixtouch sensor 80 having 5 sets of electrodes. Each set has a primaryelectrode 81C, 82C, 83C, 84C, 85C electrically interconnected with twosub-electrodes 81A, 81B, 82A, 82B, 83A, 83B, 84A, 84B, 85A, 85B arrangedon either side of an associated primary electrode 81C, 82C, 83C, 84C,85C. For example, set 82 includes primary electrode 82C andsub-electrodes 82A and 82B. Flanking sub-electrodes of each set areinterleaved with flanking sub-electrodes of adjacent sets. In thisexample, the right-most sub-electrode 81B of set 81 is interleaved withthe left-most sub-electrode 82A of set 82; the right-most sub-electrode82B of set 82 is interleaved with the left-most sub-electrode 83A of set83; the right-most sub-electrode 83B of set 83 is interleaved with theleft-most sub-electrode of set 84 and the right-most sub-electrode 84Bof set 84 is interleaved with the left-most sub-electrode of set 85. Theinterleaved pattern of the electrode sets 81-85 alters the touchresponse profiles associated with the electrode sets.

Sub-electrodes 81A, 81B, 82A, 82B, 83A, 83B, 84A, 84B, 85A, 85B of eachset 81-85 are electrically connected to each other and theircorresponding primary electrode 81C, 82C, 83C, 84C, 85C by interconnects71-75 at one end of the primary electrode 81C, 82C, 83C, 84C, 85C andsub-electrodes 81A, 81B, 82A, 82B, 83A, 83B, 84A, 84B, 85A, 85B. Thesub-electrodes 81A, 81B, 82A, 82B, 83A, 83B, 84A, 84B, 85A, 85B of eachset 81-85 may also be electrically connected to each other 81A to 81B,82A to 82B, 83A to 83B, 84A to 84B, 85A to 85B and to theircorresponding primary electrode 81C, 82C, 83C, 84C, 85C at the oppositeend by interconnects 91-95. The interleaved arrangement of the primaryelectrodes 81C, 82C, 83C, 84C, 85C and sub-electrodes 81A, 81B, 82A,82B, 83A, 83B, 84A, 84B, 85A, 85B is configured to increase an area ofcapacitive coupling associated with each primary electrode 81C, 82C,83C, 84C, 85C.

The sets of electrodes 81-85 connected to controller circuitry throughTMPs via signal lines 78. The touch area 88 of sensor 80 is surroundedon three sides by shield 89. The signal lines 78 are shielded withelectrostatic shield 89. Interconnects 91-95 may be shielded but neednot be. Primary electrodes 81C, 82C, 83C, 84C, 85C have width W_(PB) andsub-electrodes 81A, 81B, 82A, 82B, 83A, 83B, 84A, 84B, 85A, 85B havewidth W_(SB). In some embodiments, W_(PB) is greater than W_(SB), makingthe surface area of primary electrodes 81C, 82C, 83C, 84C, 85C greaterthan their corresponding electrodes 81A, 81B, 82A, 82B, 83A, 83B, 84A,84B, 85A, 85B. The larger surface area of the primary electrodes 81C,82C, 83C, 84C, 85C increases the capacitive coupling of the primaryelectrodes 81C, 82C, 83C, 84C, 85C in relation to their correspondingsub-electrodes 81A, 81B, 82A, 82B, 83A, 83B, 84A, 84B, 85A, 85B. Asillustrated in FIG. 3B, the spacing between primary electrodes is P andthe spacing between a primary electrode and a correspondingsub-electrode is D.

FIG. 3B depicts cross section BB of sensor 80, including electrode sets81-84. Overlay plate 51 has thickness 54. Touch surface 53 is on the topsurface of plate 51. Electrode 32 represents the lower electrodes of thematrix, which are substantially orthogonal to electrodes in sets 81-84.Lower electrodes are separated from top electrodes 81-84 by a dielectricspacer.

FIG. 4 illustrates touch response profiles (touch signal amplitude vs.distance of the touch from the sensing electrode) of the five primaryelectrodes 81C, 82C, 83C, 84C, 85C of sensor 80. Curves 101, 102, 103,104, and 105 are the signals measured from electrodes 81C, 82C, 83C,84C, and 85C respectively. Position sensitivity (PS) of these curves maybe calculated from Equation 1, repeated below, using the slopes ofcurves. For example, the slopes of curves 102 and 104 at point 115 are−55° and +55° respectively, resulting in PS of 2.86. Slopes of curves101 and 105 at point 115 are −13° and +13° respectively so PS to theseelectrodes is 0.46. Interpolation is possible with these slopes, but animprovement can be made by using interleaved sub-electrodes.

FIG. 5 shows touch profile responses measured on all 15 electrodes ofsensor 80, with interconnections 71-75 and 19-95 removed. Larger signals201, 202, 203, 204, 205 are measured from the primary electrodes 81C,82C, 83C, 84C, 85C. Smaller signals 201A 201B, 202A, 202B, 203A 203B,204A, 204B, 205A, 205B were measured on the sub-electrodes.

FIG. 6 shows touch profile responses measured with each of the 5electrode sets 81-85 interconnected at one end. Each of the primaryelectrodes 81C, 82C, 83C, 84C, 85C is connected to its corresponding twosub-electrodes 81A, 81B, 82A, 82B, 83A, 83B, 84A, 84B, 85A, 85B as shownin FIG. 3A. For example, primary electrode 81C is connected tocorresponding sub-electrodes 81A and 81B, primary electrode 82C isconnected to corresponding sub-electrodes 82A and 82B, primary electrode83C is connected to corresponding sub-electrodes 83A and 83B, primaryelectrode 84C is connected to corresponding sub-electrodes 84A and 84B,and primary electrode 85C is connected to corresponding sub-electrodes85A and 85B. The resulting touch response profiles 301-305 of FIG. 6 aresimilar to curves 101-105, except that each of curves 301-305 spreadsover a wider area, due to the total breadth covered by the primaryelectrodes and their corresponding sub-electrodes. This results ingreater overlap with adjacent curves, and thus greater sensitivity forinterpolation.

PS of these curves may be calculated from Equation 1, using the slopesof curves. For example, the slopes of curves 302 and 304 at point 315are −75° and +75° respectively. Slopes of curves 301 and 305 at point316 are −50° and +50° respectively, so PS is 7.46 to adjacent electrodesand 2.38 to second nearest electrodes. This compares favorably to the PSof 2.86 and 0.46 calculated for non-interleaved electrodes of the samespacing.

The use of sets of electrodes including primary electrodes and two ormore sub-electrodes interleaved with adjacent sub-electrodes increasesthe region of the capacitive coupling of the electrode sets, resultingin a larger touch active area associated with each electrode set.Further, the interleaved sub-electrodes smooth the touch signaltransition as a touch implement is moved from one electrode set to thenext.

The electrode sets may be arranged in a repetitive pattern. For example,the pattern may be repetitive, wherein the primary electrode widths aresubstantially the same for each set, the sub-electrode widths aresubstantially the same for each set, the spacing between the primaryelectrodes and sub-electrodes is substantially the same for each set andthe spacing between adjacent sub-electrodes is substantially the samefor each set of electrodes. The pattern may also be designed such thatthe capacitive coupling of a particular set of electrodes varieslinearly with distance from the primary electrode. This is advantageouswhere linear interpolation is used. In some implementations, such assensor 80 of FIG. 3A, each set of electrodes includes one level ofsub-electrodes, e.g., one primary electrode and two sub-electrodes, onesub-electrode at either side of the primary electrode. In otherimplementations, more than two sub-electrodes may be used to achieveadditional levels of sub-electrode interleaving. The additional levelsof sub-electrode interleaving need not be symmetrical with respect tothe primary electrode. For example, a set of electrodes may include twolevels of interleaved sub-electrodes on one side of the primaryelectrode and one level of interleaved sub-electrodes on another side ofthe primary electrode.

FIG. 7 illustrates a sensor 140 having five sets of electrodes 151-155having two levels of interleaved sub-electrodes 151A, 151B, 151D, 151E,152A, 152B, 152D, 152E, 153A, 153B, 153D, 153E, 154A, 154B, 154D, 154E,155A, 155B, 155D, 155E on either side of the primary electrodes 151C,152C, 153C, 154C, 155C. Each set of electrodes 151-155 has a primaryelectrode 151C, 152C, 153C, 154C, 155C and four correspondingsub-electrodes 151A, 151B, 151D, 151E, 152A, 152B, 152D, 152E, 153A,153B, 153D, 153E, 154A, 154B, 154D, 154E, 155A, 155B, 155D, 155Einterleaved at two levels with neighboring sets. For example, primaryelectrode 151C has corresponding sub-electrodes 151A, 151B, 151D, 151E.The two right-most sub-electrodes 151B, 151E of primary electrode 151Care interleaved with the two left-most sub-electrodes 152A, 152D ofprimary electrode 152C; the two right-most sub-electrodes 152B, 152E ofprimary electrode 152C are interleaved with the two left-mostsub-electrodes 153A, 153D of primary electrode 153C; the two right-mostsub-electrodes 153B, 153E of primary electrode 153C are interleaved withthe two left-most sub-electrodes 154A, 154D of primary electrode 154C;the two right-most sub-electrodes 154B, 154E of primary electrode 154Care interleaved with the two left-most sub-electrodes 155A, 155D ofprimary electrode 155C.

The widths of the primary electrodes and sub-electrodes and/or thespacing between electrodes may be selected to control the shape of thetouch response profile. Where a primary electrode has multiplesub-electrodes on each side, as in FIG. 7, the sub-electrodes on eachside of a primary electrode may be substantially equally spaced from oneanother. Alternatively the distance between adjacent sub-electrodes of aset may be varied. Increasing the distance between the electrodes of aset spreads out the touch response profile associated with the set ofelectrodes. For example, profiles 101-105 were measured with a 15 mmfinger touch implement width, W_(B)=5 mm, P_(B)=19 mm, and min. distance34=2.1 mm, (referring to FIG. 2). Profiles 301-305 were measured withthe same main electrode dimensions, (referring to FIG. 3A) W_(PB)=5 mm,P=19 mm, overlay thickness 54=2.1 mm, and sub-electrode dimensionsW_(SB)=1 mm and D=12 mm. Maximum electrode spacing is limited by thecombination of touch implement width and overlay plate thickness. Largertouch implements and a thicker overlay plate smooth out the profilesignal and allow larger distances P and D between primary electrodes andsub-electrodes.

FIG. 8 shows profiles 1301-1305 that were measured on the same electrodesets as profiles 101-105 of FIG. 4 and the same touch implement wasused, except that overlay thickness 54=0.18 mm rather than 2.1 mm. Withthis thin overlay, signal coupling to primary electrodes andsub-electrodes no longer merge together to form a smooth curve. Instead,profiles 1301-1305 vary more with touch implement position, so eachprimary electrode and each sub-electrode of a set generates a separatepeak in the profile of the set. For example, profile 1302 has peaks1320, 1321, and 1322. In addition, the thin overlay causes signals solarge that the electronic controller is overdriven, resulting in aflattening of primary peak 1321.

Profiles such as those in FIG. 8 are not necessarily desirable for mostinterpolation algorithms. In the case where an overlay thickness is 0.18mm thick, spacing among primary electrodes and sub-electrodes must bereduced proportionally.

FIG. 9 shows profiles 1401-1405 and 1410 that were measured by a 15 mmwide touch implement making capacitive contact through 2.1 mm glassoverlay to non-interleaved electrodes separated by 1 cmcenter-to-center. Electrode 1401 is a 30 AWG wire of 0.25 mm diameter.Electrodes 1402-1405 are flat, 1 mm wide. Electrode 1410 is flat, 3 mmwide. The difference in magnitude among electrodes of different widthsindicates the non-linear relationship between width and the amount ofcapacitive coupling. Differences in the amplitude among the same-widthelectrodes 1402-1405 indicate measurement error of the system.

FIG. 10 shows profiles 1501-1505 and 1510 that were measured on the sameelectrodes as shown in FIG. 9, except the capacitive contact from afinger to electrodes is made through a 0.18 mm overlay thickness. Thedifference in magnitude among electrodes of different widths indicatesthe non-linear variation of capacitive coupling as width and overlaythickness are varied. Differences in the peak intensity among thesame-width electrodes 1502-1505 indicate error of the measurementsystem.

The widths of the primary electrodes and sub-electrodes for each set maybe substantially equal or the widths of the primary electrodes may bedifferent from the widths of the sub-electrodes. In some embodiments,the width of the primary electrode is greater than the widths of thesub-electrodes to achieve the larger capacitive coupling of the primaryelectrode. In further embodiments, the width of the primary electrodemay be equal to or less than the widths of the correspondingsub-electrodes. A larger capacitive coupling of the primary electrodemay be achieved by arranging the primary electrode closer to the touchsurface, for example.

The sub-electrodes in a set may each have substantially the same widthor may have different widths. For example, the sub-electrodes fordifferent levels may have different widths as illustrated in FIG. 7. Inthis example, the primary electrodes 151C, 152C, 153C, 154C, 155C arethe widest electrodes, producing greater capacitive coupling, the firstlevel sub-electrodes 151A, 151B, 152A, 152B, 153A, 153B, 154A, 154B,155A, 155B nearest their corresponding primary electrodes 151C, 152C,153C, 154C, 155C are the next widest electrodes and the second level subelectrodes 151D, 151E, 152D, 152E, 153D, 153E, 154D, 154E, 155D, 155Ehave the narrowest widths in each set of electrodes.

Electrodes of each set are interconnected at one end by interconnects141-145. Electrodes may optionally be connected on the opposite end byinterconnects 161-165.

This is advantageous when electrodes have relatively high resistance, asis often the case when electrodes are made of transparent films such asindium tin oxide (ITO). Interconnecting each set of electrodes at bothends reduces resistance from any point on an electrode to signal lines148 because current from any point on an electrode can follow twoparallel paths to reach signal lines 148, rather than one. FIGS. 3A, 7,and 11 show examples of electrode sets interconnected at both ends.FIGS. 13C, 14, and 15 show examples of electrode sets connected at oneend. In addition, signal lines may be directly connected to both ends ofeach electrode set to provide a further reduction in resistance; i.e.161 may be connected to 141, which is directly connected to one ofsignal lines 148; 142 may be connected to 162, etc. This has thedisadvantage that additional border width 168 and/or 169 is required toroute connections between the two ends of the sensor, and additionalparasitic capacitance is added.

The two levels of sub-electrodes of sensor 140 provide additionalcontrol over the shape of touch response profiles such as thoseillustrated in FIG. 6. Additional sub-electrode levels may allow widerspacing between electrode sets, and/or lower end-to-end resistance ofeach electrode set. Multiple-level electrode sets (5 or more electrodes)may cover more of the sensor surface than single-level (3-electrode)sets, so they may be particularly advantageous when used on the bottomelectrodes of a matrix sensor. Use of non-interleaved electrodes (FIG.2B) or single-level sets for the top layer of electrodes (FIG. 3A) mayallow more space between sub-electrodes. This exposes more of the lowerlayer of electrodes for maximum capacitive coupling to lower electrodes.

In some embodiments, a sub-electrode at one edge of the touch sensor maybe interconnected with a corresponding primary electrode at an oppositeedge of the sensor. The purpose of this sub-electrode is to provide asignal for interpolation at the edge of the sensor. FIG. 11 shows onelayer of a matrix touch sensor 180 having 5 sets of electrodes. Sensor180 is identical to sensor 80 except that sub-electrode 81A has beenmoved to the right edge from the left, and sub-electrode 85B has beenmoved from the left edge to the right. The sub-electrode 81A is used forinterpolation at the right edge, and the sub-electrode 85B is used forinterpolation at the left edge of the sensor.

Each electrode may have a substantially constant width or a varyingwidth along the length of the electrode. In the examples provided inFIGS. 3A, 7, and 11 each electrode has a rectangular shape with asubstantially constant width along the length of the electrode.Electrodes having variable widths along their length may have portionsthat have various shapes, including, diamond, octagonal, hexagonal, orother geometric shapes. Some embodiments use an interleaved top layer ofelectrodes. Other embodiments use an interleaved top layer and a planarelectrode on the bottom layer. Yet other embodiments use interleaved topand bottom layers. Yet other embodiments use interleaved electrodes onone layer and non-interleaved electrodes on another layer. If two layersof electrodes are used, the top layer electrodes may have the same ordifferent widths, shapes, spacings, and/or levels or patterns ofinterleaving from the bottom layer electrodes.

In some embodiments, as is illustrated in FIGS. 12A-B and 13A-E, theshape and/or arrangement of the top layer electrodes and/or the bottomlayer electrodes may be configured to increase capacitive couplingthrough one layer of electrodes to another layer of electrodes. Forexample, the shape and/or arrangement of the primary electrodes and/orthe sub-electrodes on the top layer may be configured to increasecapacitive coupling to primary electrodes and/or sub-electrodes of thebottom layer. The shape and/or arrangement of the primary electrodesand/or sub-electrodes on the bottom layer may also be configured toincrease capacitive coupling through the top layer. In someimplementations, the top and bottom layer electrodes may havecomplementary shapes that enhance capacitive coupling as illustrated inFIGS. 13A-E.

FIG. 12A illustrates a plan view of an electrode pattern that includestop and bottom layers of electrodes. The bottom layer electrodes,comprising the substantially horizontal electrodes of FIG. 12A, arearranged in an interleaved pattern. The primary electrodes 910 haveportions configured as octagons 912 with interleaved rectangularsub-electrodes 914. In this embodiment, electrodes 920 of the top layerare not interleaved. The top layer electrodes 920, which are thevertical electrodes in FIG. 12A, include octagonal segments ofconductive material 922 with a rectangular opening in the center 924.The opening in the center 924 enhances capacitive coupling of a touch tothe sub-electrodes of the bottom layer 914. The increased capacitivecoupling through the openings 924 of the top layer electrodes is mostsignificant to the sub-electrodes of the bottom layer which lie justbelow the non-conducting centers 924 of the top layer electrodes. FIG.12B illustrates a similar touch sensor where the primary electrodes 930on the bottom layer include diamond shaped portions 932 in place of theoctagonal portions 912 of the sensor illustrated in FIG. 12A.

In some embodiments, both the top and the bottom layers may includeelectrodes having complementary shapes as illustrated in FIGS. 13A-13E.FIG. 13A is a plan view illustrating a top layer of interleavedelectrodes, FIG. 13B is a plan view illustrating a bottom layer ofelectrodes, and FIG. 13C is a plan view illustrating both top and bottomlayers. In this example, the primary electrodes of the top layer 1010include portions having an octagonal segment of conductive material 1012with an octagonal opening in the center 1014. The opening in the centers1014 promote capacitive coupling to the electrodes of the bottom layer,most significantly to the primary electrodes of the bottom layer thatlie just below the opening 1014 of the top layer 1010 primaryelectrodes. The top layer sub-electrodes 1020 are rectangular withconstant widths along the lengths of the sub-electrodes.

As illustrated in FIGS. 13B and 13C, the primary electrodes 1030 of thebottom layer include octagonal portions 1032 that are complementary withthe openings 1014 of the top layer primary electrodes 1010. Theoctagonal portions 1032 of the bottom layer primary electrodes 1030 arearranged to be vertically aligned with the openings 1014 of the primaryelectrodes 1010 of the top layer. The sub-electrodes 1040 of the bottomlayer are rectangular electrodes having constant widths along thelengths of the electrodes. FIG. 13C illustrates the interconnections1052, 1054 between the interleaved primary electrodes 1010, 1030 andsub-electrodes 1020, 1040 of the top and bottom layers, respectively.

FIG. 13D illustrates an alternate configuration of the sub-electrodes1050 of the bottom layer. In FIG. 13D, the rectangular sub-electrodes1040 of FIG. 13B are replaced by sub-electrodes 1050 that includeprotruding regions 1051. The protruding regions 1051 are complementarywith the octagonal portions 1012 of the top layer primary electrodes.FIG. 13E illustrates the plan view of a touch sensor having a top layeras illustrated in FIG. 13A and a bottom layer as illustrated in FIG.13D.

In some embodiments, the electrodes, including primary andsub-electrodes, on one or both layers may be configured as multipleconductive elements. The multiple conductive elements that make up eachelectrode may be substantially parallel, substantially equally spacedand/or have substantially equal widths. FIG. 14 shows a layer of primaryelectrodes 511C, 512C, 513C, 514C, 515C and sub-electrodes 511A, 511B,512A, 512B, 513A, 513B, 514A, 514B, 515A, 515B that are comprised ofequally spaced, equal width parallel conductive elements 510. In thisexample, the parallel conductive elements 510 have been connected tofive sets of electrodes 511-515, where each set of electrodes includesnine conductive elements 510, with 2-level interleaving with theadjacent set of sub-electrodes, (not all electrodes of the left-most andright-most sets are shown). The primary electrodes 511C, 512C, 513C,514C, 515C each comprise three conductive elements 510. The first levelsub-electrodes 511B, 512A, 512B, 513A, 513B, 514A, 514B, 515A are eachcomprised of two conductive elements 510. Second level sub-electrodes511E, 512D, 512E, 513D, 513E, 514D, 514E, 515D are each comprised ofsingle conductive elements 510. Construction of this type allows theproduction of a substrate with standardized conductive elements 510,illustrated by the vertical lines in FIG. 14, forming the electrodes.The standard substrate material may then be customized into any desiredsensor configuration by a secondary process that includes printing theelectrode interconnections 520, illustrated by the horizontal lines inFIG. 14, for example as described in commonly assigned and co-pendingpatent applications U.S. Ser. No. 11/025,559 and U.S. Ser. No.11/120,025 which are incorporated herein by reference. In someconfigurations, the electrode elements may have substantially equalwidths and the primary electrodes may comprise more electrode elementsthan the sub-electrodes. In other configurations, the electrode elementsmay not have equal widths, and/or the primary electrodes may have thesame number of electrode elements as the sub-electrodes.

The embodiments of the invention use interleaved electrodes to increasethe capacitive coupling of electrode sets. The electrode sets of thepresent invention may additionally be connected in a coding scheme tofurther reduce the number of signal lines connecting to the controller.The number of signal lines and corresponding TMPs for a touch system maybe reduced if the electrode sets are connected to the signal lines inaccordance with a coding scheme that facilitates touch locationdetermination without requiring independent access to each electrodeset. One useful coding method of arranging the electrode sets is apositional encoding scheme, which may also referred to as a uniqueneighboring scheme. In this scheme, each electrode set shares the samesignal line with several other electrode sets. The electrode sets arearranged so that each electrode set is grouped with neighboringelectrode sets. When a touch implement couples to one of the electrodesets connected to a single signal line, the touched electrode set can berecognized from other electrode sets sharing the same signal line byanalyzing the relative strengths of signals caused by the touch. Acombination of electrode sets having stronger signals may be detectedand used to identify the touch location. The physical separation betweenthe electrode sets that are connected to the same signal line must belarge enough so that a touch to the touch screen is strongly sensed byonly one electrode set among the electrode sets connected to the samesignal line. The coding scheme is selected to provide sufficientseparation between electrode sets that are attached to the same signalline to avoid confusion in determining the touch location. Exemplarycoding schemes for touch sensors are described in more detail incommonly owned U.S. Patent Publication 2003/0234771A1 which isincorporated herein by reference.

FIG. 15 shows sensor layer 1600 with 10 sets of interleaved electrodes1601, 1602, 1603, 1604, 1605, 1606, 1607, 1608, 1609, 1610 havingprimary electrodes 1601C, 1602C, 1603C, 1604C, 1605C, 1606C, 1607C,1608C, 1609C, 1610C having respectively associated sub-electrodes 1601A,1601B, 1602A, 1602B, 1603A, 1603B, 1604A, 1604B, 1605A, 1605B, 1606A,1606B, 1607A, 1607B, 1608A, 1608B, 1609A, 1609B, 1610A, 1610B. The 10electrode sets 1601, 1602, 1603, 1604, 1605, 1606, 1607, 1608, 1609,1610 are connected to five signal lines A, B, C, D, and E such that eachsignal line A, B, C, D, E is connected to two electrode sets 1601, 1602,1603, 1604, 1605, 1606, 1607, 1608, 1609, 1610. Electrode sets 1601,1602, 1603, 1604, 1605, 1606, 1607, 1608, 1609, 1610 are arranged in apositionally encoded scheme whereby each instance of adjacent electrodesets are associated with a combination of signal lines. For example,electrode set 1602 is coupled to signal line B and is adjacent toelectrode sets 1601 and 1603 coupled to signal lines A and C,respectively. The other instance of an electrode set coupled to signalline B is electrode set 1609 which is adjacent to electrode set 1608,coupled to signal line E, and electrode set 1610, coupled to signal lineD. For example, if signal lines A and B, or B and C have the strongestsignals, resulting from coupling to a touch, the touch is known to benear the left-most electrode set 1602 coupled to signal line B. Ifsignal lines B and D or B and E have the strongest signals, the touch isknown to be near the right-most electrode set 1609 coupled to signalline B.

Touch screens in accordance with embodiments of the present inventionmay be opaque or transparent, depending on their intended application.For transparent touch screens the electrodes may be formed of atransparent conductive material, such as indium tin oxide (ITO) or othertransparent conductor deposited on an insulating substrate. Forapplications that do not require transparency, electrodes may be made ofmetal or other conductive materials. Transparent touch screens are oftenused in conjunction with a display that is viewable through the touchscreen.

A method for making the touch sensors having interleaved conductorsinvolves disposing sets of electrodes on a substrate in accordance withan interleaved pattern. Each set of electrodes includes a primaryelectrode capable of producing greater capacitive coupling to a touch inrelation to capacitive coupling of sub-electrodes electrically connectedand parallel to the primary electrode. The primary electrode is disposedbetween at least two of the sub-electrodes. The interleaved pattern isconfigured to increase an effective area of capacitive couplingassociated with the set of electrodes.

FIG. 16 illustrates a touch sensing system that may incorporate thetouch sensor having interleaved electrodes as described herein. Thetouch sensing system 620 shown in FIG. 16 includes a touch screen 622having interleaved electrodes which is connected to the TMPs of acontroller 626. In a typical deployment configuration, the touch screen622 is used in combination with a display 624 of a host computing system628 to provide for visual and tactile interaction between a user and thehost computing system.

It is understood that the touch screen 622 can be implemented as adevice separate from, but operative with, a display 624 of the hostcomputing system 628. Alternatively, the touch screen 622 can beimplemented as part of a unitary system which includes a display device,such as a plasma, LCD, or other type of display technology suitable forincorporation of the touch screen 622. It is further understood thatutility is found in a system defined to include only the touch sensor622 and controller 626 which, together, can implement a touchmethodology of the present invention.

In the illustrative configuration shown in FIG. 16, communicationbetween the touch screen 622 and the host computing system 628 iseffected via the controller 626. It is noted that one or morecontrollers 626 can be connected to one or more touch screens 622 andthe host computing system 628. The controller 626 is typicallyconfigured to execute firmware/software that provides for detection oftouches applied to the touch sensor 622 by measuring signals on theinterleaved electrodes of the touch screen 622 arranged in accordancewith the principles of the present invention. It is understood that thefunctions and routines executed by the controller 626 can alternativelybe effected by a processor or controller of the host computing system628.

In one particular configuration, for example, the host computing system628 is configured to support an operating system and touch screen driversoftware. The host computing system 628 can further support utilitysoftware and hardware. It will be appreciated that the varioussoftware/firmware and processing devices used to implement touch sensorprocessing and functionality can be physically or logically associatedwith the controller 626, host computing system 628, a remote processingsystem, or distributed amongst two or more of the controller 626, hostcomputing system 628, and remote processing system.

The controller 626 typically includes circuitry 621 for measuring touchsignals sensed using the interleaved electrodes and a touch processor625 configured to determine the location of the touch using the measuredsignals. The touch sensing system 620 may be used to determine thelocation of a touch by a finger, passive stylus or active stylus. Inapplications that sense a finger touch or passive touch implement, thecontroller includes drive circuitry 623 to apply an appropriate signalto the electrodes of the touch screen 622. In some embodiments,circuitry 621 for measuring the touch signals may be incorporated intothe housing of the passive stylus. In systems using an active stylus,the active stylus generates a signal that is transferred to theelectrodes via capacitive coupling when the active stylus is near thesurface of the touch sensor.

Some components of the controller 626 may be mounted to a separate cardthat is removably installable within the host computing system chassis.Some components of the controller 626, including drive circuitry 623,sensing circuitry, or measurement circuitry 621, including filters,sense amplifiers, A/D converters, and/or other signal processingcircuitry may be mounted in or on a cable connecting the touch screen622 to the controller 626.

The foregoing description of the various embodiments of the inventionhas been presented for the purposes of illustration and description. Itis not intended to be exhaustive or to limit the invention to theprecise form disclosed. Many modifications and variations are possiblein light of the above teaching. It is intended that the scope of theinvention be limited not by this detailed description, but rather by theclaims appended hereto.

1. A capacitive touch sensing system, comprising: a touch surface; andsets of electrically connected and substantially parallel electrodesarranged in relation to the touch surface, each set of electrodesincluding a primary electrode and, electrically connected thereto by wayof interconnects, at least two sub-electrodes disposed on either side ofthe primary electrode and having a smaller surface area than the primaryelectrode, wherein the sub-electrodes of the electrode sets areinterleaved.
 2. The touch sensing system of claim 1, wherein a width ofeach primary electrode varies along a longitudinal axis of the primaryelectrode.
 3. The touch sensing system of claim 1, wherein a width ofeach sub-electrode varies along a longitudinal axis of thesub-electrode.
 4. The touch sensing system of claim 1, wherein theelectrode sets are disposed on two layers, wherein electrodes on a firstlayer include geometric elements and electrodes on a second layerinclude geometric elements complementary with the geometric elements ofthe first layer electrodes, the complementary geometric elements of thefirst and second layer electrodes configured to enhance capacitivecoupling of the second layer electrodes.
 5. The touch sensing system ofclaim 1, wherein: the primary electrode of each electrode set comprisesa first number of adjacent electrode elements having substantially equalwidth; and the at least two sub-electrodes of each electrode setcomprises a second number of adjacent electrode elements havingsubstantially equal width.
 6. A method for making a touch sensorcomprising disposing sets of electrodes on a substrate in accordancewith an interleaved pattern configured to increase an effective area ofcapacitive coupling associated with each set of electrodes, each set ofelectrodes comprising a primary electrode capable of producing greatercapacitive coupling to a touch in relation to capacitive coupling ofsub-electrodes electrically connected by way of interconnects andsubstantially parallel to the primary electrode, the primary electrodedisposed between at least two of the sub-electrodes.
 7. The method ofclaim 6, wherein the interleaved pattern is configured to shape touchresponse profiles associated with the electrode sets, each touchresponse profile representative of a relationship between touch signalamplitude and touch position relative to a particular electrode set. 8.The method of claim 6, wherein disposing the electrode sets on thesubstrate in accordance with the interleaved pattern comprises disposingthe electrode sets in a single layer.
 9. The method of claim 6, whereindisposing the electrode sets on the substrate in accordance with theinterleaved pattern comprises disposing a first portion of the electrodesets in a first layer and a second portion of the electrode sets in asecond layer.
 10. The method of claim 6, wherein the primary electrodeof each electrode set has a larger surface area than the sub-electrodesof each electrode set.
 11. The method of claim 6, wherein theinterconnects electrically connect the primary electrode andsub-electrodes of each electrode set at one end of the primaryelectrode.
 12. The method of claim 6, wherein the interconnectselectrically connect the primary electrode and sub-electrodes of eachelectrode set at both ends of the primary electrode.
 13. The method ofclaim 6, wherein disposing the electrode sets on the substrate comprisesdisposing a plurality of substantially equally spaced and substantiallyequal width electrode elements on the substrate, wherein the primaryelectrode of each electrode set includes a first number of adjacentelectrode elements and the sub-electrodes of each electrode set includea second number of adjacent electrode elements.